A Florida mom allegedly mixed her 9-month-old son’s baby formula with fentanyl, killing him, police said Wednesday. The boy was found unresponsive without a pulse on June 26, and after failed attempts from deputies to resuscitate him, he was declared dead at a Jacksonville hospital. His mother, a 17-year-old, at first told investigators that she didn’t know what happened. But her story unraveled after an autopsy revealed that the baby had enough fentanyl in his body to kill 10 people. She later admitted that she mixed her son’s formula with what she thought was cocaine, but was actually fentanyl. Nassau County Sheriff Bill Leeper couldn’t contain his disbelief during a press conference. “Who does that? What mother would do that? That’s not normal. It is sick. It’s beyond my imagination why a mother would do that to her child,” he said. The mother’s name isn’t being released, but she’s being charged with aggravated manslaughter and possession of a controlled substance.